Many particulate materials are conveniently transported by truck, although they may also be transported by railcar, barge or by other means. Trucks that are used to transport such materials commonly include a tractor and an attached trailer having a tank or other container mounted thereon. Such trailers may also be loaded on railcars or barges, or a container may be mounted directly on a railcar or barge. Frequently, these transport containers are referred to as pneumatic containers because of the pneumatic method, involving gas- or air-entrainment, by which they may be loaded and unloaded. Particulate materials that are generally transported in pneumatic containers include agricultural products such as grain, corn kernels, beans, flour, sugar, peanuts and the like, lightweight aggregate products, and intermediate products for various industrial uses such as plastic pellets or powders, coke, lime, silica gel, powdered acid resins, rare earth powders and powdered alumina.
Pneumatic containers generally include one or more product compartments that are usually cylindrical or spherical in shape in order to facilitate unloading by a method which involves pressurizing the compartments. Cylindrical or spherical product compartments are also generally easy to completely empty. Each product compartment is provided with a discharge hopper that may be generally cylindrical or conical in shape. Each discharge hopper has a material outlet at the bottom and a valve which controls the entry of material into the outlet. An unloading system is also provided which includes a blower or other mechanism for pressurizing air or another gas. The blower provides the energy required for unloading the material from the container in the form of compressed air or another gas. One end of a pressurizing gas conduit is attached to the blower and the other end to a pressurizing gas inlet in the container. Operation of the blower will compress air or gas and move it through the pressurizing gas inlet into the container, thereby increasing the pressure of the air or gas above the material in the product compartments in the container in order to assist in discharging material through the hopper outlets. One end of a material conveying conduit is also attached to the blower and extends past and connects to each material outlet so that when the product compartment has been pressurized, air or another gas may be directed into the material conveying conduit to entrain material passing through each material outlet and carry it to the discharge end of the conduit.
Pneumatic containers are commonly mounted on a frame which includes the undercarriage of a trailer. The product compartments of the container are generally enclosed by a sheet metal sheath, and the container is supported by internal rings or fully circumferential external rings and longitudinal rails. Internal rings make it difficult to wash out the inside of the container, potentially trapping product in crevices adjacent to the rings. Such trapped product may harbor bacteria that could contaminate subsequent product loads. In addition, external rings and rails contribute to increased drag coefficient, thereby resulting in reduced fuel efficiency.